EP0244249B1 - Verfahren zur Abtrennung von Schwefelwasserstoff aus Gasströmen - Google Patents

Verfahren zur Abtrennung von Schwefelwasserstoff aus Gasströmen Download PDF

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Publication number
EP0244249B1
EP0244249B1 EP87303894A EP87303894A EP0244249B1 EP 0244249 B1 EP0244249 B1 EP 0244249B1 EP 87303894 A EP87303894 A EP 87303894A EP 87303894 A EP87303894 A EP 87303894A EP 0244249 B1 EP0244249 B1 EP 0244249B1
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Prior art keywords
metal chelate
solution
amount
chelate
alkaline solution
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EP87303894A
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French (fr)
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EP0244249A3 (en
EP0244249A2 (de
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Gaines C. Jeffrey
John D. Myers
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Dow Chemical Co
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Dow Chemical Co
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/46—Removing components of defined structure
    • B01D53/48—Sulfur compounds
    • B01D53/52—Hydrogen sulfide
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
    • B01D53/1493—Selection of liquid materials for use as absorbents
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10K—PURIFYING OR MODIFYING THE CHEMICAL COMPOSITION OF COMBUSTIBLE GASES CONTAINING CARBON MONOXIDE
    • C10K1/00—Purifying combustible gases containing carbon monoxide
    • C10K1/08—Purifying combustible gases containing carbon monoxide by washing with liquids; Reviving the used wash liquors
    • C10K1/10—Purifying combustible gases containing carbon monoxide by washing with liquids; Reviving the used wash liquors with aqueous liquids

Definitions

  • the present invention relates generally to improving a process for the removal of hydrogen sulfide from gaseous streams utilizing a chelated polyvalent metal to convert the hydrogen sulfide to elemental sulfur. More particularly, the hydrogen sulfide is converted to hydrosulfide and/or sulfide salts and sulfur by contact with an aqueous alkaline solution and the polyvalent metal chelate.
  • GB-A-999,800 issued July 28, 1965, describes processes according to the pre-characterising parts of both independent claims 1 and 2. teaches the benefit of employing a high proportion of a polyvalent metal chelate in the reduced valence state in conjuction with a polyvalent metal chelate in the oxidized or higher valence state, to reduce degradation of the chelating agent in a process for the removal of hydrogen sulfide from a gas.
  • the gaseous stream is contacted with an aqueous solution containing iron complexed with an amino polycarboxylic acid in which the iron is a mixture of the higher and lower valence state.
  • the hydrogen sulfide gas is converted to sulfur by contact with the iron chelating agent in which the iron is present in the higher oxidation state.
  • the iron is reduced to the lower oxidation state.
  • the iron is converted from the lower oxidation state to the higher oxidation state in an oxidation zone and it is at this point, that, as the iron chelating agent is exposed to oxidation, there results a progressive loss of the chelating agent from the aqueous solution.
  • Precipitation of insoluble iron compounds occurs as the result of the decomposition of the iron chelate.
  • the British Patent teaches the controlled, oxidative regeneration of the iron chelate so as to prevent localized, intensive, oxidative decomposition of the chelating agent.
  • the total iron present in the iron chelate solution can be ferrous iron with the preferred proportion of ferrous iron chelate remaining in the solution after regeneration being between 20 and 50% by weight, based upon the total iron chelate present in said solution.
  • EP-A-0186235 discloses the use of a mixture of ferrous and ferric chelate in an aqueous scrubbing solution for removing hydrogen sulfide from sour gases.
  • the maximum molar ratio of ferrous chelate to ferric chelate is 0.3, with the molar range 0.1 to 0.25 being preferred.
  • the scrubbing solution can contain a selective absorbent for hydrogen sulfide and carbon dioxide and preferably has a pH in the range 6 to 7.5.
  • the characterizing feature of the process of EP-A-0186235 is that the scrubbing solution is regenerated by contact with oxygen using a plug flow contacting procedure to maintain a presence of ferrous chelate in order to inhibit degradation of the ferric chelate.
  • EP-A-0212730 discloses a process for removing H2S from a gaseous stream by employing a solubilized coordination complex of Fe(III) with nitrilotriacetic acid to oxidise the H2S to solid sulphur in a contacting zone.
  • the Fe(III) complex is present in an aqueous reactant solution which also contains a solubilized coordination complex of Fe(II) with nitrilotriacetic acid.
  • the molar ratio of the Fe(III) complex to the Fe(II) complex in the reactant solution is from 0.2 to 6.
  • EP-A-0212730 teaches that the stability of the reactants is temperature dependent, and, in particular, that the temperature of the reactant solution should be kept below the melting point of sulphur during the oxidation step.
  • the sulphur is recovered by heating the mixture in an oxygen free environment to a temperature sufficient to melt the sulphur. This produces a two phase system, the upper phase comprising a solution of solubilized iron/nitrilotriacetic acid coordination complexes, and the lower phase comprising molten sulphur.
  • the sulphur is then recovered by separating the two phases, and the reactant solution is regenerated and recycled to the contacting zone, the ratio of the Fe(III) to the Fe(II) coordination complex being from 0.2 to 6 (Fe(II) to Fe(III) ratio from 5:1 to 1:6).
  • EP-A-0215505 (priority date 23rd August 1985, filing date 15th August 1986, publication date 25th March 1987) teaches that H2S can be removed from a gaseous stream by employing an ammonium form of a coordination complex of Fe(III) with nitrilotriacetic acid to oxidise the H2S to sulphur.
  • the Fe(III) complex is present in an aqueous reactant solution which has a pH of between about 5 and about 8.5, and which also contains an ammonium form of a coordination complex of Fe(II) with nitrilotriacetic acid, and aqueous ammonia.
  • the molar ratio of the Fe(III) complex to the Fe(II) complex in the reactant solution is from about 0.2 to about 6 (Fe(II) to Fe(III) ratio from 5:1 to 1:6).
  • EP-A-0215505 further teaches that degradation or decomposition of the polyvalent iron complexes can be prevented if the aqueous reactant solution contains 0.01 mol to 4 mol of thiosulphate ion per mol of iron.
  • the process of EP-A-0215505 optionally comprises the steps of regenerating and recycling the reactant solution for further oxidation of H2S.
  • an aqueous alkaline solution of a polyvalent metal chelate especially a chelate wherein the polyvalent metal is iron, can be utilized in a continuous process for the liquid phase oxidation of hydrogen sulfide in a gas stream to elemental sulfur without substantial oxidation degradation of the chelating agent.
  • a second aspect of the invention provides a continuous process for removing hydrogen sulphide from a sour gaseous stream comprising contacting said gaseous stream with an aqueous alkaline solution having a pH of at least 7 for absorption of the hydrogen sulphide in form of hydrosulphide and/or sulphide, said solution also comprising a polyvalent metal chelate present in a higher and a lower valency state, and, during said contacting and int he same zone, introducing into the aqueous alkaline solution an oxygen containing gas to generate an amount of higher valency state metal chelate by oxidation of lower valency state metal chelate, the amount generated being effective to completely oxidise the absorbed hydrogen sulphide to sulphur, characterised in that the solution contains an alkali and in that the amount of lower valency state metal chelate present in the solution is greater than five times the amount of higher valency state metal chelate present in the solution.
  • a polyvalent metal chelate agent is present in which all or substantially all of the metal is in the lower valence state in an aqueous alkaline solution.
  • the hydrogen sulfide in the gas stream is converted to the hydrosulfide and/or sulfide by the aqueous alkaline solution.
  • a polyvalent metal chelate present in the contact zone in the higher valence state, is present in an amount of at least equal to about the stoichiometric amount in moles required to convert the hydrogen sulfide to sulfur provided the amount in moles of said lower valence polyvalent metal in said chelate is greater than 5 times the amount of said higher valence polyvalent metal.
  • the hydrosulfide and/or sulfide not converted to elemental sulfur in the contact zone are thereafter reacted in an oxidation zone wherein the lower valence polyvalent metal chelating agent from the contact zone is oxidized to the higher valence state in an effective amount in order to complete the oxidation of said hydrosulfide and/or sulfide to elemental sulfur.
  • FIGs. 1 and 2 there are shown two embodiments of the process of the invention in schematic form.
  • a separate contact zone 10 and oxidizing zone 18 is shown.
  • the zone 50 functions as both a contact zone and an oxidizing zone.
  • a process for the removal of hydrogen sulfide from a sour gaseous stream in which a hydrogen sulfide containing gas is contacted in a contact zone with an aqueous alkaline solution containing a polyvalent metal chelate.
  • a hydrogen sulfide containing gas is contacted in a contact zone with an aqueous alkaline solution containing a polyvalent metal chelate.
  • the polyvalent metal is present in the higher valence state some or all of the hydrogen sulfide is converted in the contact zone to elemental sulfur. Any hydrogen sulfide remaining is converted to hydrosulfide and/or sulfide by the aqueous alkaline scrubbing solution.
  • the alkalinity of the scrubbing solution is used to absorb the hydrogen sulfide from the sour gaseous stream and convert it to hydrosulfide and/or sulfide.
  • the contact zone in one embodiment of the invention can contain an amount up to equal to or greater than a stoichiometric amount of the polyvalent metal chelate in the higher valence state of the metal which is required to convert the hydrogen sulfide present in sulfur.
  • the lower valence polyvalent metal chelate present must be present in an amount greater than 5 times the amount of higher valance state polyvalent metal chelate present.
  • the amount of polyvalent metal chelate present in the lower valence state is preferably greater than about 10, and most preferably greater than about 30 times the amount of polyvalent metal chelate present in the higher valence state.
  • the process of the invention is operated in one embodiment of the invention in a manner contrary to the teachings of the prior art processes for hydrogen sulfide removal wherein the polyvalent metal of the polyvalent metal chelate is present in the contact zone in all or substantially all in an oxidized, or higher valence state.
  • the polyvalent metal chelate when present in the contact zone of the process of the invention all or substantially all in the lower valence state is ineffective in converting hydrogen sulfide, hydrosulfide, and/or sulfide to elemental sulfur in the contact zone but is believed to act as a scavenger for oxygen radicals which are considered to be responsible for the degradation of the chelating agent.
  • the polyvalent metal chelate Upon oxidation of the lower valence polyvalent metal chelate to the higher valence state in an oxidation zone, the polyvalent metal chelate becomes effective to convert hydrosulfide and/or sulfide to sulfur.
  • the hydrosulfide and/or sulfide formed in the contact zone by reaction of the hydrogen sulfide with the aqueous alkaline solution is thus oxidized to sulfur in the oxidation zone.
  • at least an effective amount of polyvalent metal chelate in an oxidizing or higher valence state is present in the oxidation zone.
  • Said effective amount is defined as at least a stoichiometric amount and preferably up to 5 to 10 mole percent in excess thereof.
  • polyvalent metal chelating agents particularly those in the class of polyamino polycarboxylic acids, are subject to oxidative decomposition with precipitation of insoluble iron compounds as the chelating agent is decomposed.
  • the decomposition of the polyamino carboxylic acid portion of the chelating agent is known to be accelerated in the presence of iron ions in the higher valence state.
  • Such decomposition is discussed in British Patent 999,800 and in the Canadian Journal of Chemistry , 58, No. 19 for October 1, 1980 in an article by Motekaitis et al ., The Iron (III)--Catalized Oxidation Of EDTA In Aqueous Solution .
  • the available evidence indicates that chelate degradation occurs through several mechanisms, the most important likely involving oxygen radicals. Maximizing the proportion of ferrous iron (II) to ferric iron (III) in the process of the invention has been found to minimize chelate degradation.
  • At least about a stoichiometric amount of a chelate in the higher valence state of the metal is present in the contact zone in order to convert some or all of the hydrogen sulfide to sulfur so as to achieve a greater hydrogen sulfide absorption rate.
  • the presence in the contact zone of higher valence state chelate is important, especially where the process is operated at the lower end of the pH range, in order to provide a more economical solution flow rate. Recirculation from the oxidation zone to the contact zone of the process of the invention of at least about said stoichiometric amount of higher valence form polyvalent metal chelate can be used.
  • a ferrous iron chelate is oxidized to the ferric iron chelate in the oxidation zone in an effective amount, which is sufficient to oxidize the remaining hydrosulfide and/or sulfide present in the aqueous alkaline solution fed to the oxidation zone from the contact zone, the oxidative degradation of the chelating agent in the contact zone is substantially avoided.
  • This is accomplished by the control of oxidizer conditions so as to keep the presence therein of the iron chelate in the higher valence state to a minimum while maintaining a large excess of iron chelate in the lower valence state.
  • a sour gas is introduced through line 32 into a venturi scrubber 34 so as to mix with a polyvalent metal chelate alkaline solution which enters scrubber 34 through line 29 which is fed by line 26 from pump 24.
  • the gas and liquid mixture passes into bubble tower contact zone 10 for further contact.
  • a gas essentially free of hydrogen sulfide leaves bubble tower 10 through line 12 and polyvalent metal chelate solution in admixture with hydrosulfide and/or sulfide and sulfur passes through line 14 to oxidation zone 18.
  • Air or other oxygen containing gas is fed to oxidation zone 18 through line 20 and is distributed within oxidation zone 18 by means of sparging apparatus 21.
  • Spent air or other oxygen containing gas is vented through line 16.
  • the lower valence metal in the polyvalent metal chelate solution present in oxidation zone 18 is oxidized to the higher valence state of the metal to provide at least an effective amount to convert the remaining sulfide and/or hydrosulfide present therein to sulfur.
  • the amount of oxidation of said polyvalent metal chelate is controlled so as to preferably provide an excess of at least the stoichiometric amount of polyvalent metal chelate in the higher valence state needed to convert to sulfur the hydrosulfide and/or sulfide present in said contact zone 10.
  • the polyvalent metal chelate solution comprising sulfur and all or substantially all of the polyvalent metal chelate in the reduced or lower valence state exits oxidation zone 18 through line 22 and is pumped by means of pump 24 though line 26 into line 29 and thence to the venturi scrubber 34.
  • a bypass is shown through filter zone 28 by way of line 27 for removal of at least a portion of sulfur in a sulfur recovery zone. Sulfur is removed from the system through line 30.
  • the filtered polyvalent metal chelate solution exits filter zone 28 through line 29, is joined by line 26, and is recycled thereafter to venturi scrubber 34 and then to contact zone 10.
  • FIG. 2 there is shown another embodiment of the invention in which a combined contact and oxidation zone 50 is fed through line 60 with an oxygen containing gas such as air which is distributed within said zone 50 by sparging apparatus 52.
  • Sour gas is fed through line 58 into said zone and distributed therein through sparging apparatus 54.
  • a mixture of gases, essentially free of hydrogen sulfide is discharged through vent 72.
  • a small amount of the polyvalent metal chelate solution is removed for sulfur recovery through line 56 by means of pump 62 and passes through line 64 to filter zone 68 from which sulfur is removed through line 66.
  • the polyvalent metal chelate solution is returned to the contact/oxidation zone 50 through line 70.
  • hydrogen sulfide is absorbed from the gaseous phase in a contact zone by reaction with hydroxide ion present in an aqueous alkaline solution. Hydrosulfide and/or sulfide are formed. All or substantially all of the polyvalent metal chelate can be present in the contact zone in the reduced or lower valence state of the metal.
  • the absorption capacity of the contact zone aqueous alkaline solution need not be reduced in the process of the invention where the higher valence state polyvalent metal chelate is present in at least said stoichiometric amount, provided the amount of polyvalent metal chelate present in the lower valence state of the metal is generally greater than 5 times the amount of polyvalent metal chelate present in the higher valence state of the metal.
  • one embodiment of the process of the invention provides for the use of up to about least a stoichiometric amount, based upon the hydrogen sulfide absorbed in the contact zone, of the polyvalent metal chelating agent in the higher valence state.
  • the aqueous alkaline solution is thereafter removed from the contact zone and sent to the oxidation zone wherein an effective amount of polyvalent metal chelate in an oxidizing or higher valence state is produced, said effective amount being at least a stoichiometric amount required to produce by reaction of said chelate in said higher valence state with said hydrosulfide and/or sulfide, a sulfur product and a polyvalent metal chelate product in a reduced or lower valence state.
  • the polyvalent metal chelate In order to convert the polyvalent metal chelating agent from the lower valence state to the higher valence state, in which it is effective as a reactant for the oxidation of hydrogen sulfide, hydrosulfide, and/or sulfide, the polyvalent metal chelate can be exposed to an oxygen containing gas such as air so as to promote the oxidation process. Control of the amount of air introduced in the oxidation zone allows an effective amount of polyvalent metal chelate to be present in the higher valence state or oxidized state which is sufficient to function as a reactant in the oxidation of the hydrosulfide and/or sulfide to elemental sulfur. The polyvalent metal chelate is simultaneously reduced to the lower valence state.
  • an oxygen containing gas such as air
  • the sulfur is separated in a sulfur recovery zone by conventional separation processes such as filtration, flotation, and the like and the residual aqueous alkaline solution, containing all or substantially all of said polyvalent metal chelate in the reduced or lower oxidation state, is returned to the contact zone.
  • gaseous stream treated is not critical, as will be evident to those skilled in the art.
  • Streams particularly suited to removal of hydrogen sulfide by the practice of the invention are naturally-occurring gases, synthesis gases, process gases, and fuel gases produced by gasification procedures, e.g., gases produced by the gasification of coal, petroleum, shale or tar sands.
  • gases produced by the gasification of coal, petroleum, shale or tar sands are particularly preferred.
  • coal gasification streams, natural gas streams and refinery feedstocks composed of gaseous hydrocarbon streams, waste gases, and other gaseous hydrocarbon streams.
  • hydrocarbon stream(s) is intended to include streams containing significant quantities of hydrocarbon (both paraffinic and aromatic), it being recognized that such streams contain significant "impurities" not technically defined as a hydrocarbon.
  • Streams containing principally a single hydrocarbon e.g., ethane, are eminently suited to the practice of the invention.
  • Streams derived from the gasification and/or partial oxidation of gaseous or liquid hydrocarbon may be treated by the invention.
  • the hydrogen sulfide content of the type of streams contemplated will vary extensively, but, in general, will range from 0.1 percent to 10 percent by volume. The amount of hydrogen sulfide present in the gaseous stream is not generally a limiting factor in the practice of the invention.
  • Temperatures employed in the contact zone wherein hydrogen sulfide is absorbed utilizing an aqueous alkaline solution containing a polyvalent metal chelate are not generally critical, except that the reaction is carried out at a temperature below the melting point of sulfur. Generally, the operating range temperature is from 10 to 90°C. The preferred temperature range is from 25 to 50°C and the most deferred range is 20 to 40°C. Contact times in the contact zone can generally range from 1 to 270 seconds or longer, preferably 2 to 120 seconds, and most preferably 2 to 60 seconds.
  • temperatures are not generally critical and can vary widely.
  • the oxidation zone should be maintained at substantially the same temperature as the contact zone wherein hydrogen sulfide is absorbed by an aqueous alkaline solution.
  • heat is utilized to assist the oxidation of the hydrosulfide and/or sulfide to elemental sulfur
  • cooling of the aqueous alkaline solution is not required before return of said solution to the contact zone although it is preferred that the contact zone be cooler to increase the rate of hydrogen sulfide absorption.
  • the temperatures in the oxidation zone are similar to those utilized in the contact zone. The preferred and most preferred temperatures are also similar. Pressure conditions in the contact zone and the oxidation zone can vary widely.
  • the range of operating pressure in these zones is generally atmospheric pressure to 100 atmospheres (10 MPa).
  • the preferred pressure is atmospheric pressure to 20 atmospheres (2 MPa) and the most preferred pressure is atmospheric to 3 atmospheres (0.3 MPa).
  • At high pressures the liquifaction or absorption of hydrocarbon components of the feed gas can take place.
  • the pressure-temperatures relationships involved are well understood by those skilled in the art and need not be detailed here.
  • the process operating range for pH is generally 7 to 10.
  • the preferred range is 7 to 9 and the most preferred range of pH is from 8 to 9.
  • operation at the highest portion of the range is preferred in order to operate at a high efficiency of hydrogen sulfide absorption.
  • the hydrogen sulfide is an acid gas
  • the optimum pH also depends upon the stability of the particular polyvalent metal chelate chosen. The ability of the amino acid portion of the polyvalent metal chelate to protect the metal from precipitation as an insoluble sulfide or hydroxide at high pH values will determine how high in pH the aqueous alkaline solution can be used.
  • the minimum effective amount of polyvalent metal chelate in the higher valence state which is released in the oxidation zone in one embodiment of the invention is at least a stoichiometric amount (1 mole percent chelate to 1 mole percent hydrogen sulfide), or an amount sufficient to convert all of the hydrogen sulfide present in the gas stream fed to the contact zone in the process of the invention.
  • the maximum effective amount is generally about 10 mole percent, preferably about 5 mole percent, and most preferably about 2 mole percent in excess of the stoichiometric amount of 1 mole percent chelate.
  • the lower valence polyvalent metal chelate is maintained at a concentration of greater than 5 times the amount of said chelate present in the higher valence state.
  • the amount of polyvalent metal chelate in the higher valence state which is present in the oxidation zone is controlled so as to form an amount of higher valence polyvalent metal chelate equal to or in excess of that required for conversion of the hydrogen sulfide, hydrosulfide, and/or sulfide to sulfur.
  • any oxidizing polyvalent metal chelate can be used but those in which the polyvalent metal is iron, copper, and manganese are preferred, particularly iron.
  • Other useful metals which can provide the polyvalent metal of the polyvalent metal chelate are generally those that are capable of undergoing a reduction/oxidation reaction, that is, those metals capable of being reduced to a lower valence state by reaction with hydrosulfide and/or sulfide ions and which can be regenerated by oxidation with an oxygen containing gas to a higher valence state.
  • Specific examples of useful metals include, besides the preferred metals listed above, nickel, chromium, cobalt, tin, vanadium, platinum, palladium, and molybdenum.
  • the metals, which are normally supplied as the salt, oxide or hydroxide can be used alone or as mixtures.
  • the preferred polyvalent metal chelates are coordination complexes in which the polyvalent metals form chelates by reaction with an amino carboxylic acid, an amino polycarboxylic acid, a polyamino carboxylic acid, or a polyamino polycarboxylic acid.
  • Preferred coordination complexes are those in which the polyvalent metal forms a chelate with an acid having the formula: where n is two or three; A is a C1-C4 alkyl or hydroxyalkyl group; and B is a C1-C4 alkyl carboxylic acid group.
  • a second class of preferred acids utilized in the formation of the polyvalent metal chelates utilized in the process of the invention is an amino polycarboxylic acid represented by the formula: wherein two to four of the X groups are C1-C4 alkyl carboxylic groups; zero to two of the X groups are C1-C4 alkyl groups, hydroxyalkyl groups, or and R is a divalent organic group.
  • Representative divalent organic groups are ethylene, propylene, isopropylene or alternatively cyclohexane or benzene groups where the two hydrogen atoms replaced by nitrogen are in the one or two position, and mixtures thereof.
  • polyvalent metal chelates useful in the process of the invention are readily formed in an aqueous solution by reaction of an appropriate salt, oxide, or hydroxide of the polyvalent metal and the amino carboxylic acid present in the acid form or as an alkali metal or ammonium salt thereof.
  • amino carboxylic acids include (1) amino acetic acids derived from ammonia or 2-hydroxy alkyl glycine; di-hydroxyalkyl glycine, and hydroxyl alkyl amines, such as glycine, diglycine (imino diacetic acid), NTA (nitrilo triacetic acid), 2-hydroxy alkyl glycerine; di-hydroxy alkyl glycerine, and 2-hydroxyethyl or hydroxypropyl diglycine; (2) amino acetic acids derived from ethylene diamine, diethylene triamine, 1,2-propylene diamine, and 1,3-propylene diamine, such as EDTA (ethylene diamine tetraacetic acid), HEDTA (2-hydroxyethyl ethylenediamine triacetic acid), DETPA (diethylene triamine pentaacetic acid); and (3) amino acetic acid derivatives of cyclic 1,2-diamines, such as 1,2-diamino cyclohexane N,N-
  • the buffering agents which are useful as components of the aqueous alkaline scrubbing solution of the invention are in general those which are capable of maintaining the aqueous alkaline solution at a pH generally in the operating pH range of 7 to 10.
  • the buffering agents should be water soluble at the concentrations in which they are effective.
  • suitable buffering agents operable in the process of the invention are the ammonium or alkali metal salts of carbonates, bicarbonates, or borates.
  • Examples of useful specific buffering agents within these classes of buffering agents are sodium carbonate or bicarbonate or sodium borate.
  • the carbonate or bicarbonate buffers are the preferred buffers for use in the process of the invention. These may be produced in situ by the use of an alkali in an amount suitable to provide a pH of 7 to 10, preferably ammonium hydroxide or an alkali metal hydroxide such as sodium hydroxide in the preparation of the aqueous alkaline scrubbing solution. Where the hydrogen sulfide containing feed gas contains carbon dioxide only in a minor amount, (less than about 5 percent) then the borate buffers, for example, borax or sodium borate (Na2B4O7) are useful.
  • borate buffers for example, borax or sodium borate (Na2B4O7) are useful.
  • the preferred oxygen containing gas utilized is air.
  • any inert gas may be utilized in combination with pure oxygen as an oxidizing gas.
  • the operating range of oxygen concentration in the oxidation zone is from 1 to 100 percent by volume.
  • the preferred range of oxygen concentration is 5 to 25 percent by volume, and the most preferred range is 5 to 10 percent by volume.
  • mild oxidizing conditions are preferred in the process of the invention.
  • the oxygen containing gas should be introduced to the oxidation zone in such a manner so as to disperse it throughout the aqueous alkaline solution and to minimize intense, localized oxidation.
  • the total amount of oxygen fed to the oxidation zone is dependent upon the amount of hydrosulfide and/or sulfide absorbed in the aqueous alkaline solution which is fed to the oxidation zone from the contact zone.
  • the minimum amount that can be fed to the oxidation zone is one-half mole of oxygen per mole of sulfide or hydrosulfide in the aqueous alkaline solution feed liquid.
  • the operating range of total oxygen fed to the oxidation zone is dependent upon the efficiency of oxygen mixing and absorption into the aqueous alkaline solution present in the oxidation zone. In the process of the invention, essentially all the dissolved sulfide and/or hydrosulfide present in the oxidation zone is converted to crystalline sulfur.
  • the operating range of total oxygen fed can be broad while carefully controlling the heating and oxygen concentration conditions in the oxidation zone. Over oxidation can result in the formation of undesirable thiosulfate and sulfate salts.
  • the operating range for oxygen present in the oxidation zone is generally one-half mole of oxygen per mole of sulfide or hydrosulfide up to five moles, preferably 1 to 3 moles of oxygen per mole of sulfide or hydrosulfide present in the aqueous alkaline solution fed to the oxidation zone.
  • a preferred amount of oxygen utilized is that amount which results in zero of the polyvalent metal chelate in the higher valence state leaving the oxidation zone.
  • any of the conventional methods for recovery of elemental sulfur employed in processes similar to the process of the invention can be employed in the present process.
  • sulfur can be recovered by settling subsequent to flocculation, centrifugation, filtration, flotation, and the like.
  • the method of sulfur recovery is not critical to the process of the invention. It is desirable to recover as much of the aqueous alkaline scrubbing solution as possible for recycle back to the contact zone of the process to minimize physical losses of the polyvalent metal chelating agent.
  • a hydrogen sulfide-containing gas was scrubbed continuously in a process schematically illustrated in Fig. 1.
  • An aqueous alkaline solution containing iron complexed with N-hydroxyethyl ethylenediamine triacetic acid (HEDTA) having a pH of 8.0 to 8.5 was controlled by addition of sodium hydroxide, as required.
  • the process was fully automated with computerized control and was continuously operated for 24 hours a day, 7 days a week, for several months in order to obtain the following data. Flow rates of process streams (gas and liquid) were continuously measured and recorded.
  • the temperature of the aqueous alkaline scrubbing solution was controlled, using an inline heat exchanger, to a temperature of about 40°C.
  • the hydrogen sulfide containing feed gas entering the contact zone and the vent gas from the contact zone were routinely analyzed for hydrogen sulfide content using an on stream flame photometric analyzer.
  • Samples of the aqueous alkaline scrubbing solution were routinely removed from the process for laboratory analysis including: total iron, as determined by atomic absorption analysis; ferric iron, as determined by the conventional thiocyanate photometric method; and chelate concentration, as determined by a liquid chromatographic method.
  • Inline bag filters were used for continuously removing crystalline sulfur from the aqueous scrubbing solution before passing the scrubbing solution to the contact zone. The amount of sulfur obtained in the process was determined.
  • the total chelated iron concentration in the aqueous scrubbing solution was adjusted to give a large molar excess with respect to sulfide in the contact zone for a series of runs to study the effect of ferric iron concentration on chelate degradation.
  • the ferric iron concentration was controlled at various levels in each run by controlling oxidizer conditions, that is, air flow rate and solution hold up time in the oxidizing zone. Substantially all absorbed sulfide was oxidized to crystalline sulfur in the oxidizing zone and the excess of ferric iron leaving the oxidizing zone was controlled to the desired level. Samples of the process solution were analyzed for free sulfide using a precalibrated sulfide specific ion electrode.
  • Chelating agent degradation was determined for each run and calculated as weight of chelating agent lost in comparison with weight of sulfur produced.
  • the ferric iron concentration was calculated as the mole ratio of ferric iron fed to the contact zone to the stoichiometric amount of ferric iron required with respect to the hydrogen sulfide fed to the contact zone.

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Claims (10)

  1. Kontinuierliches Verfahren zum Entfernen von Schwefelwasserstoff aus einem sauren Gasstrom, umfassend
    A) Inkontaktbringen des Gasstromes in einer Kontaktzone mit einer wässrigen alkalischen Lösung mit einem pH-Wert von mindestens 7 zur Absorption des Schwefelwasserstoffs in Form von Hydrogensulfid und/oder Sulfid, wobei die Lösung auch ein polyvalentes Metallchelat umfaßt, welches in einem niedrigen Valenzzustand und gegebenenfalls auch in einem höheren Valenzzustand vorhanden ist,
    B) danach, in einer Oxidationszone, Einbringen eines Sauerstoff enthaltenden Gases in die wässrige alkalische Lösung, um durch Oxidation von vorhandenem Metallchelat in niedrigem Valenzzustand eine Menge von Metallchelat in höherem Valenzzustand zu erzeugen, wobei die erzeugte Menge mindestens die stöchiometrische Menge ist, die erforderlich ist, um das in der alkalischen Lösung vorhandene Hydrogensulfid und/oder Sulfid zu Schwefel zu oxidieren, und danach Rückführen der polyvalentes Metallchelat enthaltenden alkalischen Lösung aus Schritt B) zurück zur Kontaktzone von Schritt A),
    dadurch gekennzeichnet, daß die Lösung ein Alkali enthält, und daß, wenn der Gasstrom mit der wässrigen alkalischen Lösung in Kontakt gebracht wird, das gesamte polyvalente Metallchelat in niedrigem Valenzzustand vorhanden ist, oder die Menge von vorhandenem Metallchelat in niedrigem Valenzzustand mehr als das fünffache der Menge von Metallchelat in höherem Valenzzustand beträgt.
  2. Kontinuierliches Verfahren zum Entfernen von Schwefelwasserstoff aus einem sauren Gasstrom, umfassend Inkontaktbringen des Gasstromes mit einer wässrigen alkalischen Lösung mit einem pH-Wert von mindestens 7 zur Absorption des Schwefelwasserstoffs in Form von Hydrogensulfid und/oder Sulfid, wobei die Lösung auch ein polyvalentes Metallchelat umfaßt, welches in einem höheren und einem niedrigen Valenzzustand vorhanden ist, und während des Inkontaktbringens und in der gleichen Zone, Einbringen eines Sauerstoff enthaltenden Gases in die wässrige alkalische Lösung, um durch Oxidation von Metallchelat in niedrigem Valenzzustand eine Menge von Metallchelat in höherem Valenzzustand zu erzeugen, wobei die erzeugte Menge wirksam ist um den absorbierten Schwefelwasserstoff vollständig zu Schwefel zu oxidieren,
    dadurch gekennzeichnet, daß die Lösung ein Alkali enthält, und daß die Menge von in der Lösung vorhandenem Metallchelat in niedrigem Valenzzustand mehr als das fünffache der in der Lösung vorhandenen Menge von Metallchelat in höherem Valenzzustand beträgt.
  3. Verfahren nach Anspruch 1 oder Anspruch 2, wobei das Verfahren umfaßt:
    a. Einspeisen der erhaltenen Schwefel enthaltenden wässrigen alkalischen Lösung in eine Schwefelrückgewinnungszone, und
    b. Entfernen aus der wässrigen alkalischen Lösung mindestens einen Teil des Schwefels, und
    c. danach Rückführen der behandelten wässrigen alkalischen Lösung zum Inkontaktbringen mit dem sauren Gasstrom.
  4. Verfahren nach einem der vorhergehenden Ansprüche, wobei das Sauerstoff enthaltende Gas Luft ist und der saure Gasstrom Naturgas, ein Kohlenwasserstoffstrom, Synthesegase, Prozeßgase oder Brenngase ist.
  5. Verfahren nach einem der vorhergehenden Ansprüche, wobei das Metallchelat ein Koordinationskomplex ist, worin das Metall mit mindestens einer Aminocarbonsäure, einer Aminopolycarbonsäure, einer Polyaminocarbonsäure oder einer Polyaminopolycarbonsäure ein Chelat bildet.
  6. Verfahren nach Anspruch 5, wobei der Chelatbildner ist:
    i. eine Aminopolycarbonsäure der Formel:
    Figure imgb0007
     worin n zwei oder drei ist, B eine C₁-C₄ Alkylcarbonsäuregruppe ist und A eine C₁-C₄ Alkyl- oder Hydroxyalkylgruppe ist oder
    ii) eine Polyaminopolycarbonsäure der Formel:
    Figure imgb0008
     worin zwei oder vier der X-Gruppen C₁-C₄ Alkylcarbonsäuregruppen sind, null bis zwei der X-Gruppen C₁-C₄ Alkylgruppen, Hydroxyalkylgruppen oder
    Figure imgb0009
     sind und R eine divalente organische Gruppe ist.
  7. Verfahren nach Anspruch 6, wobei die Aminopolycarbonsäure Ethylendiamintetraessigsäure (EDTA) oder N-2-(Hydroxyethyl)ethylendiamintriessigsäure (HEDTA) ist.
  8. Verfahren nach Anspruch 7, wobei das polyvalente Metallchelat mit der Aminopolycarbonsäure gebildet wird und das Metall Eisen ist.
  9. Verfahren nach einem der vorhergehenden Ansprüche, wobei die wässrige Lösung mindestens ein Puffermittel enthält, das fähig ist die wässrige alkalische Lösung innerhalb eines pH-Bereichs von 7 bis 10 zu halten.
  10. Verfahren nach Anspruch 9, wobei das Metall Eisen ist, das Puffermittel mindestens eines ist aus Ammonium- oder Alkalimetallsalz eines Carbonats, Bicarbonats oder Borats und das Alkali Ammoniumhydroxid oder ein Alkalimetallhydroxid ist.
EP87303894A 1986-05-01 1987-04-30 Verfahren zur Abtrennung von Schwefelwasserstoff aus Gasströmen Expired - Lifetime EP0244249B1 (de)

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US06/857,863 US4774071A (en) 1986-05-01 1986-05-01 Process and composition for the removal of hydrogen sulfide from gaseous streams

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CN104437085B (zh) * 2014-12-26 2017-01-25 中南大学 一种液相高效还原再生脱硝铁基螯合剂的方法
CN106395756B (zh) * 2016-08-31 2018-08-31 华陆工程科技有限责任公司 一种处理含氨、羰基硫、硫化氢酸性气，并进行硫磺回收的新型工艺
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